Angiographic injection equipment

ABSTRACT

An angiographic injector system for producing a controlled rate of flow of injection fluid is described. The injector has a motor-driven piston for ejecting fluid from a syringe cartridge contained within a pressure jacket. The drive motor is operated in accordance with a command voltage which is proportional to the desired rate of flow. Sensing means detects the actual rate of flow and comparison means provides an error signal which controls the motor. Compensating means allow a single control system to operate the drive motor in conjunction with syringes of various sizes, and a tripping circuit halts the motor if the flow rate exceeds the selected rate.

United States Patent [72] inventors Marlin S. Heilman Gibsonla; DonaldJones, Pittsburgh, both of Pa. [21] App1.No. 567,643 [22] Filed July25,1966 [45] Patented Nov. 30, 1971 [73] Assignee Medrad,lncorporatedPittsburgh, Pa.

[54] ANGIOGRAPHIC INJECTION EQUIPMENT 24 Claims, 4 Drawing Figs. [52]U.S.Cl 128/2 R, 128/218 A [51] int. Cl ..A61b 06/00, A61m 05/20 [50]Field olsearch 128/2, 2.05, 218, 218 A, 215:137/30, 36; 3 I 8/345, 347,309-312, 318, 349, 350; 222/55, 63, 76; 103/11, 12, 35, 36 [56]References Cited UNITED STATES PATENTS 2,627,270 2/1953 Glass 128/218 APrimary Examiner-Dalton L. Truluck Attorney-Jones & Lockwood ABSTRACT:An angiographic injector system for producing a controlled rate of flowof injection fluid is described. The injector has a motor-driven pistonfor ejecting fluid from a syringe cartridge contained within a pressurejacket. The drive motor is operated in accordance with a command voltagewhich is proportional to the desired rate of flow. Sensing means detectsthe actual rate of flow and comparison means provides an error signalwhich controls the motor. Compensating means allow a single controlsystem to operate the drive motor in conjunction with syringes ofvarious sizes, and a tripping circuit halts the motor if the flow rateexceeds the selected rate.

PATENTEUuuv so IHII SHEET 1 UF 2 //v VENTORS MARLIN 5. HE/LMA/V DONA L 0JONES BKJW ATTORNEYS ANGIOGRAPHIC INJECTION EQUIPMENT This applicationrelates, in general, to the medical science of angiography, and, moreparticularly, to injection equipment for use therein.

Angiography is a radiological technique wherein the arteries of veinsofa human or animal body are outlined by injecting suitable contrastmaterial therein, permitting X-ray photographs to be made of the veinsand arteries into which the material is injected. Because of itsdiagnostic value, angiography is enjoying increased use and many newinstrumentation needs have arisen.

The contrast material used in angiography must be injected into thedesired vein or artery close to the area to be photographed andimmediately prior to making the photograph, for the flow of bloodtherethrough generally dissipates the contrast material very quickly.The material must, therefore, be injected through a long thin tube,generally called a catheter, to the vascular site of interest. Pressuresas high as 1,000 p.s.i. have been used to accomplish this injection and,traditionally, the controlling injection variable has been the pressuresetting on the injector used to supply the contrast material. However,the injector pressure setting is only one of the factors whichdetermines contrast material flow rate, other factors being the internaldiameter of the catheter, the catheter length, the contrast mediumviscosity, and the configuration of the flow path, and it is the rate offlow of the contrast medium through the catheter in which theangiographer is interested. It is highly important that these factors berecognized, for failure to do so, and resultant reliance on pressuresetting alone, can produce unpredictable flow rates under varyingconditions. At best, such variations in flow rate reduce the quality ofthe X-ray photographs, while at worst may actually damage the vein orartery into which the material is being injected. It is therefore anobject of this invention to provide a flow control injector system inwhich the operator can directly select the rate of contrast mediuminjection without regard to the many variables which affect flow rate.

Accurate knowledge of the contrast material discharge rate from thecatheter tip is required in order to insure that the angiographicprocedure is safe, for excessively high flow rates may causeconsiderable damage. Another object of this invention, therefore, is toprovide means for monitoring and recording the actual pressure that isbeing used to accomplish the injection. A related object of theinvention is to provide means for protecting the patient from suchdamaging flow rates by providing a rate trip network in the controlcircuitry of the present injector equipment, whereby the injection willbe stopped in the event of a system failure that might lead to aninjection rate higher than the operator command rate.

In the design of an injection system, a number of practicalconsiderations should be taken into account. Space around an X-ray tableis limited. Further, the catheter entrance point in the body of thepatient, and, consequently, the ideal position of the injector tip withrespect to the patient is variable, and is a function of patient size,position and the exact puncture site. For these reasons, a smallinjector that may be freely positioned in space around the X-ray tablesurface is a desirable end. With increased experience, angiographershave learned to place catheter tips in selective small flow areas whereinjection rates of l to ccs per second are adequate for radiologicalopacification of the vessels under study.

An injector to satisfy the foregoing selective angiographic needs shouldbe very small, should be injection rate-controlled and should be capableof being hand held or freely positioned around the injection site. It istherefore an additional object of the invention to provide anangiographic injector system which is compact and easily movable, yet iscapable of providing a rate-controlled flow of sufficient volume to meetthe needs of the art.

Inasmuch as the techniques of angiography may be applied in many partsof the body, all of which require different flow rates and which mayrequire different quantities of contrast material, it follows that thereis a need for a series of injectors all of which are injectionrate-controlled, but differing in size and work capacity. However, sucha series of injectors would multiply the cost of angiography, and makeit less useful as a diagnostic tool. In order to avoid the duplicationof such a series of injectors, and thus substantially to reduce the costof such a series, the present invention provides a common power sourceand control system for use with a plurality of injectors and cartridgesof differing size and capacity.

Prior art injectors, as well as that of the present invention, areelectrically operated, and as a result an electrical potential isestablished in the injector. The prior injector art does not attempt toelectrically insulate the contrast medium from this electricalpotential. Rather, attempts are made to maintain the patient at the samepotential as the injector. However, recent evidence has shown thatvoltages and currents as low as millivolts and 100microamperes'transmitted from an injector through a catheter to theheart may cause a fatal heart condition known as ventricularfibrillation. It is an object of this invention to avoid this danger bypackaging the contrast material in nonconductive plastic and rubbersyringes to insulate the patient from the injector. It is a furtherobject of this invention to protect these plastic syringes fromexplosion during a high pressure injection by protecting them with apressure jacket.

These and other objects and features of the invention will becomeapparent to those skilled in the art from the following description of apreferred embodiment thereof, taken in conjection with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a control circuit for a flow ratecontrolled injector system;

FIG. 2 illustrates in graphical from the operation of the rate tripcircuit of FIG. 1;

FIG. 3 is a side plan view, partly in cross section and partly brokenaway, of an injector suitable for use with the control circuit of FIG.I; and

FIG. 4 is a cross-sectional side plan view of a modified syringe andsupporting pressure jacket suitable for use in the injector of FIG. 3.

Turning now to a consideration of the circuit of FIG. I, there isillustrated a control system by means of which the operator of theinjector system may select an injection flow rate that will be deliveredand maintained regardless of the various flow attenuating factorsmentioned above. A command voltage directly proportional to the desiredinjection rate is established by adjustment of a potentiometer 10 havinga linear resistor portion 12 connected between a source of referencevoltage 14 and a ground point and a slidable arm 16. Movement of theslidable arm by the operator determines the magnitude of the voltageapplied through a line 18 to an amplifier 20, and thus determines theflow rate, motion of the arm causing a varying flow rate, while aselected position produces a selected constant rate. A tachometergenerator 22, which is mechanically linked to the shaft of the injectordrive motor 24 by way of linkage 26, generates a feedback voltage at itsterminals that is directly proportional to the actual injection rate,for as will be described hereinafter, the rate of flow must be directlyproportional to the speed of motor 24 because of the nature of itsdirect drive mechanism. This feedback voltage, which has a polarityopposite to that of the command voltage, is applied by way of line 28 toa generator compensating voltage divider 30 comprised of resistors 32and 34 connected in series across generator 22. This voltage dividerpermits compensation of the control circuitry for different injectorswhich may have different mechanical linkages and generator outputvoltages. Selector switch 36 permits selection of the desired voltagelevel for application through line 38 to a scale factor voltage divider40 which compensates the feedback voltage for various syringe crosssections, thus permitting the user of different sized syringes with aselected injector device. Voltage divider 40 is comprised of the seriesarrangement of resistors 42, 44 and 46 connected between line 36 andground, and a selector switch 48 for applying the desired voltage levelthrough line 50 to the input of amplifier 20. Since the feedback andcommand voltages are of opposite polarity, the algebraic sum of themagnitudes of these voltages at the input of amplifier constitutes anerror signal which corresponds to the difference between the desired andthe actual injection rates.

The voltage dividers 30 and 40 are provided because it has been foundthat considerable savings in the cost of injector systems as well as inthe space used by such systems, in addition to increased versatility ofthe system, can be effected if the injector system consists of a singlepower and control unit which services different size injectors which, inturn are capable of using different size syringes. Voltage divider 30will then compensate for feedback voltage differences between, forexample, a large, high-pressure injector and a small, hand-heldinjector. Voltage divider 40 will compensate for cross-sectionaldifferences in the syringes used. To provide this versatility, thefeedback voltage from the generator 22 is scaled by various constantsthat correspond first, to the generator voltage output per linearvelocity unit of the piston used to drive fluid out of the syringe, andsecond, to the injection rate of the fluid per linear velocity unit ofthe piston travel. An example of the first compensating factor involvesthe use of an injector unit which produces a higher generator feedbackvoltage per unit piston travel velocity than the setting of the controlunit which is to be used with the control unit. Voltage divider 30permits compensation for such an event, thus allowing interchangeabilitybetween control units and injectors, or interchangeability of injectorswith a given control unit. If resistors 32 and 34 are chosen so thatR34/R32+R34 equals the ratio of the lower to higher generator voltageoutputs per velocity unit of piston travel for two injector units, thenthey will be interchangeable in the control unit.

The injection rate from a syringe is directly related to the pistonvelocity multiplied by a scale factor which corresponds to the area ofthe syringe piston i.e., to the diameter of the syringe. The voltagesignal which represents the actual injection rate can be held within thedesired limits of accuracy, even though syringes of differentcross-sectional areas are used. This is done by means of scale factorvoltage divider 40. In the illustrated embodiment, with switch 36 in theposition shown, the voltage divider is set for the largest of threesyringes having different cross-sectional areas, and provides themaximum voltage output. By positioning switch 48 between resistors 42and 44, the feedback voltage is proportional in injector flow rate for asyringe of smaller cross section. To maintain this proportion, therelationship R44+R46IR42+R44+R46 must equal the ratio of thecross-sectional area of the smaller syringe to the larger syringe. Astill smaller syringe may be used if the voltage between 44 and 46 ispicked up; thus, with a feedback voltage signal exactly proportional tothe injection rate, different injectors utilizing different syringes maybe controlled by a common control and power module.

The error signal which appears at the input of high gain amplifier 20 isamplified and fed through line 52 to the base of transistor 54. Thistransistor acts as a buffer amplifier between amplifier 20 and the basesof parallel-connected power transistors 56, 58, 60 and 62. Thecollectors of the power transistors are connected to a common lowimpedance power source at 64, and the emitters are each connectedthrough current limiting, low resistance, forward-biased diodes 66, 68,70 and 72, respectively, to a common line 74. The current limitingdiodes are provided to prevent excessive emitter degeneration. Line 74is connected through contact 76 of the on-off relay coil 78 and thencethrough line 80 to the armature of motor 24. As illustrated in FIG. 3,the motor may be a permanent magnet, direct current, torque type, havinga printed circuit armature. The return motor lead is connected by line82 through a resistor 84 and a diode 86 to ground.

Utilizing the linear relationship which exists in this type of motorbetween the motor output torque and the input current, the voltage drop,due to the armature current, which appears across resistor 84, will bedirectly proportional to motor output torque and thus to the pressuregenerated by the injector. Diode 86 is chosen such that its voltage dropcorresponds to the amount of motor output torque taken up by themechanical friction of the injector. The voltage across resistor 84 maythen be measured at terminals 88 and 90, and used for pressure sensingand recording purposes.

In operation, the rate of rotation of motor 24, which rate isproportional to the actual injection flow rate from the syringe, ismeasured by means of a generator 22, producing a rate voltage. Thisinjection rate voltage is compared to a command voltage representing thedesired injector rate, and any error signal is amplified and used tocontrol the conductivity of the parallel power transistors 56, 58, 60and 62 connected in series with the motor to control its torque. Thecontrol system responds to an error signal to insure that the torqueexerted by the motor on the piston of the syringe is sufficiently greatto produce the desired flow characteristics regardless of variations inflow attenuation in the injector or the catheter.

Should the control system fail, an over-rate condition might result thatcould deliver an excessive flow of the contrast medium to the patient.To protect against this possibility, a rate trip circuit is provided asfollows. A potentiometer 94, having resistor portion 96 and sliding arm98, is ganged by means of mechanical linkage 100 with the injector ratecommand potentiometer 10, but differs from element 10 in that it has anexponential, rather than a linear, response curve and, further, has adecreasing voltage output with clockwise rotation of slidable arm 98instead of the increasing voltage with clockwise rotation of ann 16 usedin potentiometer 10.

The conceptual basis for the rate trip circuit is illustrated in FIG. 2,wherein curve A represents the exponential output of potentiometer 94with clockwise rotation of its slidable arm, while curve B representsthe linear output of potentiometer 10 with clockwise rotation of itsslidable arm. Curve C represents the product of curves A and B.

Resistor portion 96 of potentiometer 94 is connected through lines 102and 50 to the input ofamplifier 20, and thus the voltage appearing atthis input is applied to resistor portion 96. The output voltage onslider arm 98, therefore, is the product of the settings of arms l6'and98, which product is represented by curve C of FIG. 2. Resistor 104 isconnected in series with potentiometer 94 in order to maintain an outputvoltage on arm 98 that is above ground, so that the voltage representedby curve C does not fall to zero when the injection command voltage isat its maximum value.

The output appearing on arm 98 is applied through line I06 to theemitter of a unijunction transistor 108. This transistor type isutilized because of its extremely low emitter current when in the offcondition and because, at a predictable threshold voltage (indicated bycurve D in FIG. 2), which equals a known fraction of the interbasevoltage, the transistor 108 will fire and produce a voltage pulse onelectrode 0 which is fed through a diode 112 to the control electrodeI14 of a silicon controlled rectifier (SCR) 116. The SCR is thustriggered into a self-latching on" condition, allowing current to flowthrough relay coil and normally closed switch 122 to ground from voltagesource 124. Energization of relay coil 120 shifts its normally closedcontact 126 to open the current path from source 124, through contact126, through line 128, through master on-off" switch 130 and throughrelay coil 78 to ground. This deenergizes coil 78, allowing contact 76to open and halt the injection. Opening of switch 122 allows the SCR 116to return to its nonconductive state, thus permitting relay coil 120 tobe deenergized and relay coil 78 to be reenergized. This resets the ratetrip circuit and conditions the in jector control system for furthergeneration. Diode 112 allows only a positive pulse from transistor I08to trigger the SCR 116. The unijunction transistor 108 is biased by aresistor 132 connected between electrode 134 and voltage source 124 andby a resistor 136 connected between electrode 110 and ground.

By selecting appropriate values for reference voltage sources 14, and124, the characteristics of potentiometers l0 and 94 and the value ofresistor 104, one can specify the shape of curve C (FIG. 2) which, undernormal operational conditions will be a known percentage betow thresholdcurve D.

Curve D is, in turn, a function the operating characteristics ofunijunction transistor 108, and the value of resistors 132 and 136.However, should an overrate condition occur through a control systemfailure, the voltage seen by the arm 98 of potentiometer 94 would riseto the threshold voltage of the unijunction transistor 108, firing thetransistor and activating the trip mechanism to stop the injection. Analternative method of activating the unijunction is to compare thecommand rate voltage with the feedback voltage in a differentialamplifier, the output of this amplifier triggering the unijunctiontransistor when the feedback signal exceeds the command signal by apresent amount.

Turning now to a consideration of the structure of an injector devicesuitable for use with the control system above described, there isillustrated in FIG. 3 an injector syringe mechanism 152 which isparticularly designed for hand-held use. The injector mechanism isconstructed for lightness and compactness, without sacrificing therequired power, and thus is driven by direct current permanent magnetmotor 24 having a printed circuit armature 154. The shaft 156 of themotor is drivingly coupled to a threaded screw shaft 158 for rotationwith the motor armature 154. Threadedly engaging shaft 158 for rotationwith the motor armature 154. Threadedly engaging shaft 158 is a ball nut160 which is prevented by pin 162 from rotating, but which is free tomove axially along shaft 158, the pin sliding in a guide slot 164 formedin a guide bar 166 supported in the housing 168 of the injector 150. Theaxial movement of ball nut 160 in response to rotation of threaded shaft158 converts the rotary motion of motor 24 to linear motion. Ball nut160 is connected to a piston tube 170 which moves with the ball nutalong shaft 158. The outer end of the tube is supported, during itslinear motion, by an oil seal 172 secured in an opening 174 at one endof housing 168. Piston tube 170 abuts directly against a piston headsupport member 176, which, in turn, provides mechanical support for arubber piston cap 178. A syringe, or cartridge, 180 is mounted on theinjector housing 168 by means of an internally threaded nut 182 adaptedto engage external threads on the end of the housing 168. Nut 182 has acentrally located aperture 184 which receives the syringe and a sealmember 186 to permit an airtight fitting on the end of the housing. Aflanged portion 188 is provided on the end of the syringe which facesthe housing to facilitate a tight seal between sealing members 174 and186 when nut 182 is tightened.

The internal diameter of the syringe and the external diameter of piston176 are selected to provide the clearance required to permit the flangededge 190 of rubber piston cap 178 to seal the interior of the syringe.It will be apparent that different sizes of syringes will requirepistons having varying diameters, but the construction of this mechanismis such that the various sizes are easily connected to the injectordrive mechanism. The aperture in nut 182 is sufficiently large to permitlarger syringes than that illustrated, while by providing smallerdiameter syringes with sufficiently large flanges, they can be used withthis equipment as well. Piston member 176 and cap 178 may be driven in aforward direction (toward the right as viewed in FIG. 3) by piston tube170 without any mechanical connection being made between the piston andthe tube. This arrangement is often used where it is essential toprevent reversal of the motion of the piston. Alternatively, piston 176may be connected to piston tube 170 by means of screws 192, to permitboth forward and reverse driving of the piston. It will be apparent thatforward motion of the piston will expel fluid or any other matter withinthe syringe 180, such as contrast medium 194. If the piston is attachedto the piston tube 170, reverse driving can be used to fill the syringeof the reference voltage 124,

is attached to the injector drive mechanism.

The broken-away portion of motor 24 illustrates, in addition to armature154, the arrangement of the permanent magnet 196. In operation, directcurrent is commutated to the armature conductors, an the resultantalternating magnetic field interacts with the stationary magnetic fieldof the permanent 415* with the desired amount of contrast material whilethe syringe magnet to produce torque on shaft 156. Gears 198 and 200provide a mechanical linkage of known gearing ratio between the motorshaft and tachometer generator 22. The use of a printed circuitarmature, permanent magnet torque motor allows maximum power for minimumsize and makes practical a hand-held injector much smaller thanconventional electromechanical injectors.

Where greater injection power is required than can be delivered by thehand-held unit, a larger injector unit may be provided and mounted, forexample, upon a suitable base member. Such a unit would require a morepowerful motor and thus would not, as a practical matter, be a hand-heldunit. However, both injectors would use the same power and control unit,being connected to that unit through suitable multiconductor connectors.It is contemplated that the power and control unit would be mounted, forexample, in an instrument console adjacent an X-ray table, with aconnector jack located at or on the table. A series of injectors wouldthen be available for various uses, each one being plugged into theconnector jack as needed. If desired, each injector may be connected tothe power unit through some common and some individual conductors sothat the proper compensating resistors would automatically be connectedin circuit upon connection of a particular injector.

When the small, hand-held injector mechanism is used, the pressuresinvolved are relatively low, in the neighborhood of p.s.i. and adisposable plastic syringe or contrast medium cartridge may be used.However, when greater injector power is required, such containers areentirely inadequate, and they tend to explode long before the pressuresof 800 p.s.i. used in angiography are encountered. This tendency hasprevented the use of plastic containers in angiography, the acceptedmaterials being glass for the smaller units and stainless steel for themore powerful units. This type of construction made the use ofdisposable containers out of the question, and required reuse, with itsattendant danger of infection. The present invention overcomes theproblem of container explosion and permits the use of disposablesyringes or cartridges by providing the modified syringe mountingillustrated in FIG. 4, wherein a pressure jacket 210 is utilized toprevent the enclosed syringe 212 from bursting when injection pressuresin excess of the strength limitations of the syringe are used. Thepressure jacket is made to fit exactly the syringe, cartridge or ampulebeing used in the injector. This exact fit is obtained by making apositive mold of the syringe, the mold preferably being of metal. Ahigh-strength, transparent plastic, such as styrene, acrylicpolycarbonate or epoxy, is formed around the metal mold to a thicknesssufficient to withstand the anticipated pressure. A circumferentialflange is formed around the molded plastic to provide a bearing surfacefor the longitudinal forces exerted during injection. Preferably thesyringe is slightly tapered toward the discharge end so that it caneasily be inserted into and removed from the jacket. It will be apparentthat the pressure jacket can be machined to the proper fit, if desired,but the molding process is preferred. With the internal dimensions ofthe jacket exactly corresponding to the outside dimensions of thesyringe, the syringe is protected against the pressure induced by thedriving of piston 176 against the resistance offered by a restrictedflow path connected to the syringe tip 214.

Although prior automatic injectors have illustrated fluid containersresting in jackets of various types, these prior jackets have been nomore than positioning devices designed to align the containers with theinjector devices. Since the prior art contemplated low flow rates at lowpressures, and did not anticipate the art of angiography, the containerdevices were not intended to withstand high pressures, and were notcapable ofdiiing so.

By making the pressure jacket of a high strength, transparent moldedplastic material, the operator of the device not only may visuallymonitor the progress of the piston and the amount of fluid remaining inthe syringe, but may also inspect the contrast medium for air bubblesand the like. The jacket is mounted on the external threads of housing168 by means of a connecting nut 216 having internal threads 218. Acentral aperture 220 in nut 216 receives the pressure jacket 210, theconnecting nut abutting against shoulder 222 of the jacket to force thesyringe against housing 168. An elastic bearing member 224 is interposedbetween nut 216 and the bearing surface of shoulder 222 for the purposeof evenly distributing the transmission of longitudinal force. Syringe212 is provided with a flange 226 which abuts against housing 168 whenproperly seated, as described with respect to syringe 180 in FIG. 3.However, this flange serves an additional purpose in the presentembodiment in that it is designed to extend a short distance out of thepressure jacket, leaving a small space 228 to allow the syringe to begrasped by flange 226 for removal from the pressure jacket.

The construction of the pressure jacket permits the use of a disposable,preloaded syringe of light weight glass or plastic, providing a quick,convenient method of loading an injector while at the same timeproviding insurance against the transmission of infection from onepatient to another. Although the syringe shown in the accompanyingdrawings does not include a plunger means, but relies on the injectorplunger 170 to drive the contrast medium out, it will be apparent thatthe injector can be modified to accept syringes which are manufac turedwith a plunger. Such a construction would permit the manufacture of adisposable plastic syringe, prepackaged to contain the contrast medium,which could be used for manual injections, could be used in the small,hand-held injector, or could be used in the larger injector afterinsertion in a pressure jacket.

Although the syringes in FIGS. 3 and 4 are shown without closure meanson the outlet tips, it will be apparent that appropriate means would beprovided for a prepackaged syringe. it is preferred that the outlet tipsalso be provided with Luer- Lok fasteners for easy attachment ofcatheters and the like.

Thus, there has been provided a compact, inexpensive injection apparatusdesigned for use in angiography. This invention recognizes that themajor factor in the injection of contrast fluid is the maintenance of aconstant flow rate, rather than of a constant pressure, and the systemis accordingly directed to an injector apparatus and control circuitcapable of producing this type of operation. The result is anangiographic injector having improved operating characteristics overprior art devices, but which eliminates the complexity and bulk of theprior art. The invention also recognizes that on occasion a variation inflow rate may be desired, and thus there is provided a command voltagewhich is proportional to the desired flow. This command voltage may bederived from the slide arm of a potentiometer, or from some othersuitable source, and may be varied in either direction. The system willrespond to any changes in the command voltage to produce a correspondingvariation in the flow rate, and it will be apparent that the flow ratewill thus be a function of the command voltage. These, and such othermodifications of the described embodiment as will become apparent tothose skilled in the art, are within the spirit and scope of the presentinvention as defined by the following claims.

I claim:

1. In an injector system for producing a controlled rate of flow ofinjection fluid for use in angiography and having an injector includingsyringe means for said fluid, movable piston means for ejecting saidfluid from said syringe means, a drive motor for moving said piston,electrical control means including command means for producing a commandsignal which is a function of a desired rate of fluid flow, sensingmeans for producing a second signal which is a function of the actualinjection flow of said fluid, and means for comparing said command andsecond signals to produce a resultant signal for operating said drivemotor at a selectable, controlled rate to produce a desired flow offluid whereby the rate of flow of said injection fluid will besubstantially independent of flow-attenuating factors in the path ofsaid fluid, the improvement comprising electrical circuit meansresponsive to said control means for stopping said drive motor andthereby automatically tenninating the flow of said fluid upon theoccurrence of a condition within said system that could result in anexcessive rate of flow of said fluid.

2. The system of claim 1, wherein said circuit means is responsive to anoverrate condition, said circuit comprising means for producing athreshold signal in response to said overrate condition and gating meansresponsive to said threshold signal for thereupon disabling said drivemotor.

3. The system of claim 2, wherein said means for producing a thresholdsignal comprises potentiometer means connected to said command means andto said sensing means.

4. The system of claim 3, wherein said potentiometer means comprises anonlinear resistor having a first movable arm, said first arm beingelectrically connected to said gating means, said command meansincluding a linear potentiometer having a second movable arm, said firstand second movable arms being mechanically interconnected.

5. The injector system of claim 4, wherein said circuit means furtherincludes normally closed relay means for controlling said drive motor,and silicon controlled rectifier means in series with said relay means,said rectifier means being connected to and responsive to the operationof said gating means to open said normally closed relay means todeenergize said drive motor.

6. The injector system of claim 1, wherein said control means is mountedin a control cabinet separate from said injector, said control meansbeing connected to said injector through flexible electrical conductormeans, said injector being sufficiently small and compact to facilitateuse as a hand-held unit.

7. The injector system of claim 6, wherein the drive motor for saidinjector is a direct current, permanent magnet, torque-type motor havinga printed circuit armature to provide a small, lightweight, compactinjector.

8. The injector system of claim 1, the improvement further comprisingsignal generator means responsive to the operation of said motor forproducing said second signal, and scale factor means for maintainingsaid second signal proportional to the injection flow of said fluid forvarious cross sections of said syringe means, whereby said system can beused with a variety of syringes.

9. The injector system of claim 8, wherein said scale factor meanscomprises selectively variable voltage divider means.

10. The injector system of claim 1, the improvement further comprisingsignal generator means on said injector responsive to the operation ofsaid motor for producing said second signal, and said control meansfurther including generator compensating means connected to saidgenerator for maintaining said second signal proportional to theinjection flow of fluid for various injectors and their correspondingsignal generators, whereby said system may be used with a variety ofinjectors.

11. The injector system of claim 10, further including scale factormeans for maintaining said second signal proportional to the injectionflow of said fluid for various cross sections of said syringe means,whereby said system can be used with a variety of syringes.

12. The injector system of claim 1, the improvement further comprisinghousing means for said injector and threaded shaft means within saidhousing mechanically connected to said drive motor for rotationtherewith, ball nut means engaging the threads of said threaded shaft,means mounted in said housing for preventing said ball nut fromrotating, where by rotation of said drive motor moves said ball nutalong the axis of said threaded shaft, piston tube means extending alongthe length of said threaded shaft and having an end portion extendingbeyond the end of said threaded shaft, said end portion abutting saidpiston to drive said piston along the axis of said syringe in responseto the movement of said ball nut,

13. The injector system of claim 12, said injector further includingremovable connector means between said end portion of said piston tubeand said piston, whereby said piston tube can be connected to saidpiston for driving said piston in two directions, said piston tube beingnormally disconnected to permit said piston to be driven only in adirection to eject said fluid from said syringe.

14. The injector system of claim 13 wherein said sensing means furtherincludes compensating means for maintaining said second signalproportional to said rate of flow for various mechanical linkagesbetween said drive motor and said piston.

15. The injector system of claim 1, the improvement further comprisingdisposable syringe means for said injector, said disposable syringemeans including a disposable cartridge containing said fluid to beejected and a transparent pressure jacket adapted to receive saidcartridge and said piston means, said pressure jacket preventingdeformation of said cartridge when said system is operative to applypressure to said fluid to produce said fluid flow, a housing forsupporting said piston means, and means for removably connecting saiddisposable syringe means to said housing, said last-named meansincluding retainer means threadedly engaging said housing and having acentral aperture adapted to receive said pressure jacket, said pressurejacket having a peripheral shoulder against which said retainer meansabuts to hold said pressure jacket and housing in assembledrelationship, whereby said pressure jacket can be removed from saidhousing for replacement of said disposable cartridge.

16. The injector system of claim 15, further including electricallyinsulating means interposed between said housing and said syringe andsaid syringe means being electrically nonconductive, whereby electricpotentials on said housing are isolated from said fluid.

17. The injector system of claim 15, wherein said piston means comprisesa piston head support and a flexible piston cap mounted on said support,said cap being replaceable to pennit said piston means to be adapted tothe internal diameter of said syringe means.

18, The injector system of claim 17, the improvement further comprisingsignal generator means responsive to the operation of said motor forproducing said second signal, and scale factor means for maintainingsaid second signal proportional to the injection flow of said fluid forvarious cross sections of said syringe means, whereby said system can beused with a variety of syringes.

19. The injector system of claim 1, the improvement further comprisingmeans for producing a voltage proportional to the output torque of saiddrive motor, whereby the pressure developed in said injection fluid canbe monitored.

20. The injector system of claim 19, wherein said means for producing avoltage proportional to the output torque of said drive motor comprisesa resistor in series with the armature of said motor, said voltage beingmeasured across said resistor and being proportional to said fluidpressure.

21. The injector system of claim 20, wherein said drive motor is adirect current, permanent magnet, torque-type motor having a printedcircuit armature for moving said piston means.

22. In an injector system for producing a controlled rate of flow ofinjection fluid for use in angiography and having an injector includingsyringe means for said fluid, movable piston means for ejecting saidfluid from said syringe means, a drive motor for moving said piston,electrical control means including command means for producing a commandsignal which is a function of a desired rate of fluid flow, sensingmeans for producing a second signal which is a function of the actualinjection flow of said fluid, and means for comparing said command andsecond signals to produce a resultant signal for operating said drivemotor at a selectable, controlled rate to produce a desired flow offluid whereby the rate of flow of said injection fluid will besubstantially independent of flow-attenuating factors in the path ofsaid fluid, the improvement comprising electric circuit means includinga resistor connected to said drive motor for producing a voltageproportional to the output torque of said drive motor, said voltagebeing measured across said resistor and being proportional to said fluidpressure.

23. The injector system of claim 22, wherein said drive motor is adirect current permanent magnet, to torque-type motor having a printedcircuit armature, said resistor being connected in series with saidarmature.

24. The injector system of claim 22, wherein said syringe means iselectrically nonconductive and includes a disposable cartridge and atransparent pressure jacket adapted to receive said cartridge, saidcartridge containing a prepackaged quantity of said fluid to be ejected,and said pressure jacket holding said cartridge in operative positionwhile said injecting pressure is generated in said cartridge.

1. In an injector system for producing a controlled rate of flow ofinjection fluid for use in angiography and having an injector includingsyringe means for said fluid, movable piston means for ejecting saidfluid from said syringe means, a drive motor for moving said piston,electrical control means including command means for producing a commandsignal which is a function of a desired rate of fluid flow, sensingmeans for producing a second signal which is a function of the actualinjection flow of said fluid, and means for comparing said command andsecond signals to produce a resultant signal for operating said drivemotor at a selectable, controlled rate to produce a desired flow offluid whereby the rate of flow of said injection fluid will besubstantially independent of flow-attenuating factors in the path ofsaid fluid, the improvement comprising electrical Circuit meansresponsive to said control means for stopping said drive motor andthereby automatically terminating the flow of said fluid upon theoccurrence of a condition within said system that could result in anexcessive rate of flow of said fluid.
 2. The system of claim 1, whereinsaid circuit means is responsive to an overrate condition, said circuitcomprising means for producing a threshold signal in response to saidoverrate condition and gating means responsive to said threshold signalfor thereupon disabling said drive motor.
 3. The system of claim 2,wherein said means for producing a threshold signal comprisespotentiometer means connected to said command means and to said sensingmeans.
 4. The system of claim 3, wherein said potentiometer meanscomprises a nonlinear resistor having a first movable arm, said firstarm being electrically connected to said gating means, said commandmeans including a linear potentiometer having a second movable arm, saidfirst and second movable arms being mechanically interconnected.
 5. Theinjector system of claim 4, wherein said circuit means further includesnormally closed relay means for controlling said drive motor, andsilicon controlled rectifier means in series with said relay means, saidrectifier means being connected to and responsive to the operation ofsaid gating means to open said normally closed relay means to deenergizesaid drive motor.
 6. The injector system of claim 1, wherein saidcontrol means is mounted in a control cabinet separate from saidinjector, said control means being connected to said injector throughflexible electrical conductor means, said injector being sufficientlysmall and compact to facilitate use as a hand-held unit.
 7. The injectorsystem of claim 6, wherein the drive motor for said injector is a directcurrent, permanent magnet, torque-type motor having a printed circuitarmature to provide a small, lightweight, compact injector.
 8. Theinjector system of claim 1, the improvement further comprising signalgenerator means responsive to the operation of said motor for producingsaid second signal, and scale factor means for maintaining said secondsignal proportional to the injection flow of said fluid for variouscross sections of said syringe means, whereby said system can be usedwith a variety of syringes.
 9. The injector system of claim 8, whereinsaid scale factor means comprises selectively variable voltage dividermeans.
 10. The injector system of claim 1, the improvement furthercomprising signal generator means on said injector responsive to theoperation of said motor for producing said second signal, and saidcontrol means further including generator compensating means connectedto said generator for maintaining said second signal proportional to theinjection flow of fluid for various injectors and their correspondingsignal generators, whereby said system may be used with a variety ofinjectors.
 11. The injector system of claim 10, further including scalefactor means for maintaining said second signal proportional to theinjection flow of said fluid for various cross sections of said syringemeans, whereby said system can be used with a variety of syringes. 12.The injector system of claim 1, the improvement further comprisinghousing means for said injector and threaded shaft means within saidhousing mechanically connected to said drive motor for rotationtherewith, ball nut means engaging the threads of said threaded shaft,means mounted in said housing for preventing said ball nut fromrotating, where by rotation of said drive motor moves said ball nutalong the axis of said threaded shaft, piston tube means extending alongthe length of said threaded shaft and having an end portion extendingbeyond the end of said threaded shaft, said end portion abutting saidpiston to drive said piston along the axis of said syringe in responseto the movement of said ball nut.
 13. The injector system of claim 12,said injector further including removabLe connector means between saidend portion of said piston tube and said piston, whereby said pistontube can be connected to said piston for driving said piston in twodirections, said piston tube being normally disconnected to permit saidpiston to be driven only in a direction to eject said fluid from saidsyringe.
 14. The injector system of claim 13 wherein said sensing meansfurther includes compensating means for maintaining said second signalproportional to said rate of flow for various mechanical linkagesbetween said drive motor and said piston.
 15. The injector system ofclaim 1, the improvement further comprising disposable syringe means forsaid injector, said disposable syringe means including a disposablecartridge containing said fluid to be ejected and a transparent pressurejacket adapted to receive said cartridge and said piston means, saidpressure jacket preventing deformation of said cartridge when saidsystem is operative to apply pressure to said fluid to produce saidfluid flow, a housing for supporting said piston means, and means forremovably connecting said disposable syringe means to said housing, saidlast-named means including retainer means threadedly engaging saidhousing and having a central aperture adapted to receive said pressurejacket, said pressure jacket having a peripheral shoulder against whichsaid retainer means abuts to hold said pressure jacket and housing inassembled relationship, whereby said pressure jacket can be removed fromsaid housing for replacement of said disposable cartridge.
 16. Theinjector system of claim 15, further including electrically insulatingmeans interposed between said housing and said syringe and said syringemeans being electrically nonconductive, whereby electric potentials onsaid housing are isolated from said fluid.
 17. The injector system ofclaim 15, wherein said piston means comprises a piston head support anda flexible piston cap mounted on said support, said cap beingreplaceable to permit said piston means to be adapted to the internaldiameter of said syringe means.
 18. The injector system of claim 17, theimprovement further comprising signal generator means responsive to theoperation of said motor for producing said second signal, and scalefactor means for maintaining said second signal proportional to theinjection flow of said fluid for various cross sections of said syringemeans, whereby said system can be used with a variety of syringes. 19.The injector system of claim 1, the improvement further comprising meansfor producing a voltage proportional to the output torque of said drivemotor, whereby the pressure developed in said injection fluid can bemonitored.
 20. The injector system of claim 19, wherein said means forproducing a voltage proportional to the output torque of said drivemotor comprises a resistor in series with the armature of said motor,said voltage being measured across said resistor and being proportionalto said fluid pressure.
 21. The injector system of claim 20, whereinsaid drive motor is a direct current, permanent magnet, torque-typemotor having a printed circuit armature for moving said piston means.22. In an injector system for producing a controlled rate of flow ofinjection fluid for use in angiography and having an injector includingsyringe means for said fluid, movable piston means for ejecting saidfluid from said syringe means, a drive motor for moving said piston,electrical control means including command means for producing a commandsignal which is a function of a desired rate of fluid flow, sensingmeans for producing a second signal which is a function of the actualinjection flow of said fluid, and means for comparing said command andsecond signals to produce a resultant signal for operating said drivemotor at a selectable, controlled rate to produce a desired flow offluid whereby the rate of flow of said injection fluid will besubstantially independent of flow-attenuating factors in the path ofsaid fluid, thE improvement comprising electric circuit means includinga resistor connected to said drive motor for producing a voltageproportional to the output torque of said drive motor, said voltagebeing measured across said resistor and being proportional to said fluidpressure.
 23. The injector system of claim 22, wherein said drive motoris a direct current permanent magnet, to torque-type motor having aprinted circuit armature, said resistor being connected in series withsaid armature.
 24. The injector system of claim 22, wherein said syringemeans is electrically nonconductive and includes a disposable cartridgeand a transparent pressure jacket adapted to receive said cartridge,said cartridge containing a prepackaged quantity of said fluid to beejected, and said pressure jacket holding said cartridge in operativeposition while said injecting pressure is generated in said cartridge.